1. Field of the Invention
The present invention relates to modular industrial automation appliances and, more particularly, to a modular industrial automation appliance and method for transmitting messages via a backplane bus system of the modular industrial automation appliance.
2. Description of the Related Art
Industrial automation systems are used for monitoring, controlling and regulating technical processes, particularly in the realm of production, process and buildings automation, and allow operation of control devices, sensors, machines and industrial installations, where the operation is intended to be effected as autonomously and independently of human interventions as possible. On account of a constantly increasing importance of information technology for automation systems that comprise numerous networked control or computer units, methods for reliably providing functions distributed over an automation system to provide monitoring, control and regulatory functions are becoming increasingly important.
Interruptions in communication links between computer units in an industrial automation system or automation appliances can lead to undesirable or unnecessary repetition of transmission of a service request. These repeated service requests cause additional workload for communication links in the industrial automation system, which can lead to further system faults or errors. Furthermore, untransmitted or incompletely transmitted messages can prevent an industrial automation system from changing to or remaining in a safe operating state, for example. This can finally lead to failure of a complete production installation and to costly production outage. A particular set of problems in industrial automation systems regularly results from signaling traffic containing a relatively large number of, but relatively short, messages, which intensifies the above problems.
EP 1 188 293 B1 discloses an interface module for a programmable logic controller, where the interface module allows transmission of data requests by a communication appliance or a computer unit outside an industrial automation system to the programmable logic controller, such as by Internet. The interface module comprises a processor, having a realtime operating system, a communication network interface and a backplane bus driver for a backplane bus system of the programmable logic controller. Furthermore, a dual protocol stack, which comprises a first and a second protocol stack, and a client control process are implemented in the interface module. The client control process is used to communicate with the dual protocol stack and the backplane bus driver and to initiate data requests. In addition, a server control process is provided to communicate with the dual protocol stack and the backplane bus driver and to respond to data requests. Furthermore, a protocol control process is used to communicate with the dual protocol stack and the backplane bus driver and to retrieve and respond to requests sent to the protocol stack. While the first protocol stack is provided for non-time-critical messages, time-critical messages are handled by the second protocol stack.
US 2004/0114591 A1 describes a programmable logic controller that comprises a backplane bus system and modules connected to the backplane bus system that communicate via the backplane bus system using the Internet communication protocol (IP). In this case, each module has a dedicated IP address.
In order to transmit messages from different subnetworks between two IP-compatible modules, which are connected to a backplane bus system and each of which has an associated subnetwork, via the backplane bus system on an IP basis, it would be fundamentally possible for each IP-compatible module to have a dedicated IP stack provided and for the backplane bus system to be operated as a dedicated subnetwork. Here, a separate IP address on the backplane bus system and routing functions will need to be provided for each IP-compatible module. Message transmission between two subnetworks via the IP-compatible modules and the backplane bus system would thus always prompt two complete IP stacks to be processed, specifically when changing to the backplane bus system and when changing from the backplane bus system.